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  • High-Precision Photometry for Exoplanet Observations N E W T E C H N I Q U E S F O R P E R F O R M I N G H I G H - P R E C I S I O N P H O M E T R I C M E A S U R E M E N T S O F E X T R A - S O L A R P L A N E T S , M I N O R P L A N E T S , A N D VA R I A B L E S TA R S U S I N G S M A L L T E L E S C O P E S

    J E R R Y H U B B E L L A S S I S T A N T D I R E C T O R M A R K S L A D E R E M O T E O B S E R V A T O R Y ( M S R O ) V I C E P R E S I D E N T O F E N G I N E E R I N G , E X P L O R E S C I E N T I F I C , L L C .

    Rappahannock Astronomy Club Meeting, October 17, 2018

  • Introduction – Jerry Hubbell

    • Jerry Hubbell is currently the Vice President of Engineering for Explore Scientific, LLC. and the Principle Engineer heading the team on the development of the PMC-Eight™ mount control system.

    • Retired Dominion Nuclear Instrumentation and Controls Engineer with over 35 years of experience in the Nuclear and Electric Utility business.

    • The Assistant Director for the Mark Slade Remote Observatory (MSRO).

    • The Assistant Coordinator for Topographical Studies, Lunar Section of the Association of Lunar and Planetary Observers (ALPO).

    • Author of 2 books published by Springer Books and available on Amazon.com. Scientific Astrophotography: How Amateurs Can Generate and Use Professional Imaging Data (2012) and Remote Observatories for Amateur Astronomers: Using High-Powered Observatories from Home (2015)

  • Presentation Topics

    • Quick Overview of Photometry and Doing Photometric Measurements

    • Why Do High-Precision Photometry?

    • Exoplanet Observations by Amateur Astronomers

    • Follow-up Ground Based Exoplanet Observations

    • High-Precision Minor Planet Light-curve Measurements

    • High-Precision Variable Star Light-curve Measurements

    • High-Precision Photometric Measurement Errors

    • Sources of Photometric Measurement Errors

    • How to Minimize the Total Photometric Measurement Error

  • Presentation Topics

    • New Instruments and Techniques for Doing High-Precision Photometry

    • Defocus Method

    • Diffuser Method

    • MSRO Diffuser Instrument Test Program

    • TESS Follow-up: Ground-based Observations

    • QUESTIONS?

  • Quick Overview of Photometry and Doing Photometric Measurements

    • Astronomical Photometry is the measurement of the brightness of celestial objects

    • In the 1970’s amateur astronomers used analog photoelectric photometers (scintillation tubes) with a fixed aperture size to measure stellar object brightness.

    • In the mid 1990’s professional techniques using CCD cameras were adopted by amateurs and software was developed for PC’s to do the required analysis.

  • Quick Overview of Photometry and Doing Photometric Measurements

    • The original idea using the photoelectric photometer was to measure a circular area encompassing the star, known as the aperture, and subtract the measured value of the sky background with the same aperture. This general technique became known as Aperture Photometry.

    • The simplest type of Aperture Photometry is Differential Aperture Photometry. This is where you measure 2 objects, assuming the comparison object is of fixed brightness, and subtract the Target Object from the Comparison Object brightness.

    • This Differential measurement takes care of any small changes that occur between samples by assuming that each frame is small enough to see the change occur for the Target Object and the Comparison Object.

  • Quick Overview of Photometry and Doing Photometric Measurements

    • In the 1970’s amateur astronomers used analog photoelectric photometers (scintillation tubes) to perform Aperture Photometry.

    • In the mid 1990’s professional techniques using CCD cameras to perform Aperture Photometry were adopted by amateurs and software was developed for PC’s to do the required analysis.

  • Aperture Photometry Aperture diagram showing object aperture, sky aperture, and object annulus for measuring the sky background and object brightness.

  • Quick Overview of Photometry and Doing Photometric Measurements

    • The Aperture Photometry technique was changed when CCD imaging was adopted to make the measurements more accurate.

    • There were 2 major changes to the technique when CCD imaging was adopted:

    • Instead of using a background aperture that could be located anywhere on the image, a background annulus was used to capture the local background signal to the object being measured.

    • Image calibration data was also applied to the data (light) frames to further refine the accuracy of the measurement when using CCD cameras.

    • Once light frames are calibrated then the observer can do the measurement of the star brightness in ADU counts by subtracting the annulus value from the object aperture value.

  • Photometric Measurement of a Minor Planet This is an example of a measurement of the brightness of a minor planet using an analysis tool

  • Quick Overview of Photometry and Doing Photometric Measurements

    • This general technique is applicable to measuring point-source celestial objects including Stars, Minor Planets, and Exoplanets.

    • This general technique is the starting point for refining and improving the accuracy of the measurement

    • For best results you should use an astronomical imaging camera that include a Thermo-Electric Cooling (TEC) system and is a monochrome camera that DOES NOT have a Color Filter Array (CFA) installed.

    • For specific scientific measurements, broadband or narrowband filters may be placed in front of the imaging chip. A V-Band filter is a very common filter used in photometric measurements

  • SBIG ST2000XM CCD TEC camera on Main Instrument at MSRO This shows the main imaging camera at the MSRO. This system is a Thermo-Electrically Cooled camera system with integrated filter wheel system.

  • Why Do High-Precision Photometry?

    • High-Precision Photometry is defined as a higher precision object brightness measurement using enhanced instruments or techniques, or both.

    • The long-held standard for amateur photometric measurements is to obtain a precision of ± 0.01 mag or about 1% error.

    • High-Precision Photometry is defined as obtaining a total precision of less than half of that, or < ±0.005 mag or as it is also known as: milli-mag error. 1 milli-mag is equal to ±0.001 mag or 1/1000 mag.

    • The main reason for doing High-Precision Photometry is to detect object light-curve variations at the milli-mag level.

    • This is necessary when doing photometric measurements of Exoplanets, Variable Stars, and Minor Planets.

  • Exoplanet Observations by Amateur Astronomers

    • Exoplanet observations made by amateurs use the Transit Method. In this method we watch for the Exoplanet to pass in front of its parent star.

    • Most Exoplanets discovered orbit stars that are magnitude 7 – 15. Of these, amateurs can observe Exoplanet transits around stars in the 7 – 10 magnitude range.

    • Jupiter size exoplanets provide a signal change of at least 1% which is typically the amount of error for an amateur observation.

    • To not just detect, but to measure accurately the time of ingress, mid-point, and egress of an exoplanet, and also the depth of the transit, a high-precision measurement must be performed.

  • MSRO HAT-P-30/ WASP-51 b Exoplanet Observation The observation of exoplanet HAT- P-30/WASP-51 b by Bart Billard and Jerry Hubbell in January 2018 using the MSRO Main Instrument.

  • Follow-Up Ground Based Observations of Exoplanets

    • There is a need for ground based follow-up observations of NASA Mission observations for the Kepler and the recently launched TESS Missions.

    • These follow-up observations will rely on professionals with the large telescopes, but also on those interested and capable amateur astronomers with the equipment, skills, and knowledge of how to perform these observations and also analyze the data gathered during these observations

  • High-Precision Minor Planet Light-curve Measurements

    • There is also a need for improved Minor Planet light-curve measurements to further refine their 3D shape models and rotation rates to further characterize the population.

    • These high-precision measurements will allow amateurs to demonstrate the value that we can bring to the study of the formation of the solar system.

  • High-Precision Variable Star Light-curve Measurements

    • Doing High-Precision Variable Star measurements will allow you to detect and measure the small fluctuations in a star’s brightness to detect star spots, and other stellar behaviors that could give you further insight into the life-cycle of stars.

    • These high-precision measurements will also allow amateurs to demonstrate the value that we can bring to the study of the formation of these stars and perhaps their local star systems.

  • High-Precision Photometric Measurement Errors

    • High-Precision Photometric Measurement Errors determine how precise we need to be in our measurements to not only detect, but accurately me